Conventionally, a drive unit such as a motor is used in an electrically controlled throttle apparatus to control a throttle valve to be in a predetermined throttle position in accordance with an accelerator position of an accelerator pedal stepped by a driver. According to an electrically controlled throttle apparatus disclosed in JP-A 10-047520, JP-A 2001-263098 and JP-A 2001-303983, a bore wall part and a motor housing part are integrally molded of a resinous material to construct a throttle body. Besides, according to JP-A 09-032590 and JP-A 11-132061, a throttle body has an outer pipe and an inner pipe that are coaxially arranged with each other to construct an integrally molded double-pipe structure, in which the inner pipe receives a throttle valve.
FIGS. 6 and 7 are perspective views showing a conventional electrically controlled throttle apparatus, for example. In the electrically controlled throttle apparatus, a throttle body 100 has a bore wall part 103 and a motor housing part 104. The bore wall part 103 is constructed with a cylindrical-shaped bore outer pipe 101 and a cylindrical-shaped bore inner pipe 102 that are coaxially arranged each other to construct a double-pipe structure. The motor housing part 104 receives a drive unit such as a motor that is heavy in weight. The bore wall part 103 includes the bore inner pipe 102 receiving a throttle valve 105. Therefore, both of the bore wall part 103 and the motor housing part 104 become heavy. Accordingly, when a connecting member 106, which connects the bore wall part 103 and the motor housing part 104, is additionally provided, the connecting member 106 needs to be rigid enough to support the heavy components. When the bore wall part 103, the motor housing part 104 and the connecting member 106 are integrally molded of a resinous material, the connecting member 106 may be formed to be thick in order to be rigid. When the connecting member 106 is molded, molecular orientation is caused by a resinous flow, and fiber included in a filler material may be oriented in a particular direction. Besides, the housing part 104 may contract in the molding process. Accordingly, circularity of the inner cylindrical periphery of the bore inner pipe 102 may be degraded. In this case, interference may arise between the throttle valve 105 and the bore inner pipe 102 over a rotation range of the throttle valve 105 from its full close position to its full open position. Furthermore, a gap, which is formed between the inner cylindrical periphery of the bore inner pipe 102 and the outer circumferential periphery of the throttle valve 105 when the throttle valve 105 is in the full close position, may become larger than a predetermined degree. Accordingly, airtightness may be degraded when the throttle valve 105 is in the full close position, and leakage of intake air increases in an idling operation of the engine.